1. Field of the Invention
This invention relates to the field of automated inspection systems, and in particular to an inspection and selection device for examining transparent or translucent returnable glass bottles and the like, selection being based upon the detection of optical patterns, for example indicating dirt, foreign material on or in the glass, proper filling of full bottles, or breakage. According to the invention selection is also based on the extent of scuffing, for detection of excess bottle wear.
2. Prior Art
A wide variety of bottle inspection systems are known in the art, including systems intended to inspect the top lip, bottom or sidewalls of bottles and hollow containers. Sidewall inspection is shown, for example, in U.S. Pat. Nos. 3,439,178--Rottmann; 3,886,356--Gomm, et al.; 3,932,042--Faani, et al.; 4,136,930--Gomm, et al.; 4,170,417--Tourres; 4,172,524--Holm, et al.; 4,280,624--Ford; 4,376,951--Miyazawa; 4,378,494--Miller; and 4,414,566--Peyton, et al. The methods and apparatus disclosed in these patents include the use of plural cameras and video processing. Various light sensing and signal processing techniques are used in efforts to detect everything from cracks to movable foreign material suspended in filled bottles. Nevertheless, even in view of this wide variety of disclosures, the one and only type of automated bottle inspection system that is sufficiently cost-effective and reliable for general use in the industry today is the type of system that inspects only the cap-receiving lips and possibly also the bases of bottles.
Known base and/or lip-examining devices are effective and practical, probably because the procedure for detection of defects and the type of defects are much less complicated than in sidewall inspection. The lip and base can be readily examined in plan view. At least the lip portion, which is carefully dimensioned to begin with in order to sealably receive a cap, must have no defect at all. Defects in the base or lip portion that justify rejection, specifically chips and cracks, are typically gross defects that are readily detectable. Unlike inspection of bases and lips, inspection of sidewalls requires examining for progressive wear as well as for gross defects. Bottle inspection devices to date have been too expensive or unable to exercise the necessary judgment for inspection of all bottle areas, lip, bottom and sidewall, which has until now required a human inspector.
In bottle inspection systems, video signal processing is used as a means to detect occurrences of contrasting light and dark in a bottle sidewall. The references mentioned above include devices which use the light and dark indication to sense the edge of bottles, and also to sense the presence of defects, which appear as contrasting dark spots on a light background, and sudden level changes in a video signal. Such systems can detect opaque defects and cracks in the lip or base, and also at least in the center of view of a sidewall. Unfortunately, even if the views are optically enlarged an/or multiplied by rotating the bottle or the like, such defects are not the only problem in sidewall-inspection systems.
In the case of returnable glass bottles such as soft drink bottles, beer bottles, and the like, after a number of cycles through bottling and use, the handling of the bottle causes damage in the form of scuffed or abraded surfaces of the bottle. The typical bottles are conical on an upper half and generally cylindrical on a lower half, the cusp between the conical and cylindrical part defining an exposed contact area against which the bottle is abraded in regular expected handling. Similar damage is expected on the lower-most edge of the bottle. These scuffing areas become more and more clouded (i.e. relatively more diffuse) as a bottle wears. At some point, the extent of scuffing becomes unacceptable; but until then, a scuffed bottle is still acceptable for reuse. A human inspector will exercise judgment in gauging the degree of bottle wear. In an automated system to detect wear, the simple detection of scuffing is not enough to achieve accuracy of selection comparable to a human inspection.
Other defects occur in bottles that are such that a human will miss. These should also be detected, but they do not show up in a video signal as a simple dark spot or the like. These include the presence of residual water remaining in a bottle after cleaning, the presence of trapped crumpled cellophane (e.g. clear cellophane from a cigarette wrapper) and the like. Problems with detecting these defects are aggravated by other defects or potential defects such as scuffing, and are also aggravated if the detection system is to be used with rippled or colored translucent bottles such as green or brown-colored bottles, as well as with clear ones.
Prior art systems have been unduly expensive. Moreover, although effective in detecting discrete attributes such as opaque spots and cracks, known inspection systems have not been effective with segregating for continuously-varying progressive defects and potential defects such as scuffing. Furthermore, the mechanical complication of inspection systems that has heretofore been required to account for even such variations as the alignment of the bottle label, differences in bottle dimensions and problems with positioning, have made prior art devices impractical for general use except for limited examination of lips and bases.
The present invention incorporates known lip and base inspection techniques, but has overcome many of the defects of prior art sidewall inspection systems by using a plurality of cameras and one or more associated video processors to separately examine upper and lower areas of the bottle from angularly-spaced views. Edge detection (i.e., contrast detection) techniques are used to define inspection windows in the views that expand the inspection area to the maximum but exclude edges and label areas, regardless of the bottle orientation. Views are backlighted and are angularly spaced more than 180 degrees such that centrally-located inspection windows in the video image, viewing through both the opposite sidewalls of the container, expose substantially all the defects present.
Separate selection standards are applied for a given bottle to normally-scuffed areas and open inspection areas, selection being based upon not only opacities, but also correlation of features in the regions and upon statistical analysis of the light and dark levels of the individual pixels in the image. Preferably, six video cameras are used for sidewalls, three for angularly-spaced elevation views at two levels and each providing, for example, a 256.times.240 matrix of pixels. The gray level at each of the pixels is detected to one of 256 separate levels of light to dark. Strobe lights or momentarily-opened camera shutters are used freeze the image of each of the moving bottles for inspection without mechanically stopping them. Preferably, sequential frozen frames of the bottle are recorded as it moves along continuously. The video cameras can be angularly spaced around the bottle, or linearly spaced along the bottle conveyor and combined with a means for turning the bottle disposed between the stations. Even given suppressing data adjacent the bottle edges in each view, the cameras provide useful data at a high angle of incidence to the bottle surfaces for the lip, base and substantially the entire circumference. Notwithstanding the substantial resolution of the video system, statistical examination of the pixel gray levels, together with correlation of the results for different areas, provides an effective bottle inspection device of modest expense.
The lack of general application of bottle sidewall inspection systems to bottling operations has been due to considerations of both effectiveness and expense. The expense to be considered is more than monetary. Currently, bottling plants use human inspectors to examine bottles moving continuously along a conveyor at speeds up to 250 bottles per minute. This job is boring, difficult and dangerous in that so many bottles stream past the inspector's fixed gaze and the view of the bottles is so hypnotizing that it shortly becomes impossible to detect even the relatively small proportion of bottles which have gross defects such as chips and opaque areas. One inspector may last only 20 minutes until relieved. Even a fresh inspector has no real hope of detecting subtleties.
Full-time human staffing of an inspection job represents an overhead expense that is not justifiable if at least comparable selection success can be obtained automatically. Furthermore, the proximity of the human inspector to the stream of fast-moving bottles is downright dangerous, as the bottles are often impelled against one another and sometimes shatter from thermal cycling from the upstream hot water and steam washing apparatus. Nevertheless, in the prior art, systems have not been available which could dependably exercise the judgment regarding progressive defects such as scuffing of bottle surfaces necessary to remove bad bottles from the good.